Just to add my 2 cents. My dog is a six year old Shih tzu cross, had him three years. Always had a patch on his lower back ("blackheads" in the pores and on the hair). Not obvious unless clipped short.
I would paint the area with chlorhexidine and forget about it until the next clipping. A few months back I noticed dried blood. The area has started to ulcerate and spread up his back. The area is itchy and he does not like you touching it.
Now I had to look more carefully, many possible reasons (and there can be primary and secondary causes):
5 Fleas and tics
As the affected area was on his back where soap is applied when bathed, I changed to a low allergenic shampoo and reduced the frequency of baths from 2 weekly to 6 weekly (he is not a smelly dog! ).
-> No change after three months, getting worse so we discounted an allergic reaction (although we did not try an antihistamine).
We then hit him with a round of antibiotics and chlorhexidine wash.
That cleaned up the skin infection but no improvement beyond that.
So when on holidays for a week and upon return and his next bath the condition had worsened. He starting to loss hair and the skin quite ulcerated and bleeding.
Okay, off to the vet (the vet is useless, her diagnosis was flea bite dermatosis but at least we got another round of antibiotics).
So we clipped the area so we an see it better and started the another round of antibiotics and chlorhexidine wash.
After two days the skin was looking better so we painted the area with borax and peroxide solution with a cotton swab.
After the treatment I examined the cotton swab and the remaining discoloured solution under a mag-light (my eyesight is not very good anymore) in a white plastic container. Although the mag-light is only x2 I could see a couple of the mites wiggling in the solution (tiny black carrots a fraction of a millimeter in length).
That night the skin looked better and some "blackheads" where now "whiteheads".
The next day he skin was a bit scaly. After the second treatment I could only see only dead mites in the contaminated solution. An hour or so later, some of his "blackhead" pores had opened up.
So it is working very well so far. Not all the blackheads are gone but they are disappearing.
We intent to do a full dip of all our dogs in the next few days.
I chose to use borax and peroxide over other remedies because they are both safe to use on "your own" skin.
Borax and Hydrogen Peroxide
You may call it mange, or any other name that describes the itching, biting, redness that your pet may be going thru. This really bothered me.... To see my pet suffering, each day seemed to be worse for her, then reading about mange, I tried the borax(20 mule team and hydrogen peroxide this mixture saved my dogs skin, and my mind. You dont rinse this off, and when mixed well doesnt create a mess. Just use small towels to do this. It may take 2 separate applications, but it was well worth it. my pets hair returned, &she healed nicely.